1. Field of the Invention
The present invention generally relates to radio communications systems and specifically relates to distribution apparatuses, terminal apparatuses, systems, and methods.
2. Description of the Related Art
Wide bandwidths are necessary for conducting communications at high speed. However, it is difficult to secure wide frequency bandwidths which are common throughout the world since various radio communications systems are in operation. Thus, a technique is being studied in which are used multiple frequency bandwidths, each of which is provided with a frequency utilization priority, and in which multiple radio communications systems use the same frequency bandwidth according to the priority. Moreover, it is difficult to secure a frequency bandwidth which can be used in common throughout the world, so that it is necessary to select, at each country, one from multiple candidates. Thus, a terminal apparatus needs to have, in accordance with a region used in, a unit which identifies a radio communications system which is in operation at a region to which the terminal apparatus belongs. However, with a large number of ultra wideband radio communications systems in use, a large consumption power and/or a long identification time is needed to realize a function which identifies a radio bandwidth which can be used. Moreover, in an environment in which frequencies are shared for use, a low-priority radio communications system (below called an “additional system”) conducts communications while using the same frequency bandwidth such as to ensure that interference is not caused on a high-priority communications system (below-called a “priority system”). Such a technique includes a technique which calculates and identifies an interference amount caused on the priority system using a propagation loss between the priority system and the additional system, and a technique which controls a transmission power of the additional system according to the interference amount identified. Moreover, a traffic amount at a time of communications by the priority system may be taken into account to calculate an allowable interference amount and to control the transmission power of the additional system. For example, the additional system may be controlled such that, in a time zone with a small traffic of the priority system, the allowable interference amount is increased, so that it is operated with a maximum transmission power which is larger than that in a time zone with a large traffic of the priority system.
When using such a technique, a frequency utilization method is dynamically changed, so that the terminal apparatus must always utilize a function which identifies a radio communications system and a frequency bandwidth which can be used.
Thus, as a way to respond to a dynamic change of the frequency utilization method, a cognitive pilot channel (CPC) is being proposed which distributes, to all of the radio communications systems in operation in each of regions, information such as frequency and radio technology used within each of the regions. The cognitive pilot channel may be applied to eliminate a process of scanning basic parameter information of a radio communications system to which a terminal apparatus can connect to. Moreover, by applying the cognitive pilot channel, changing some of parameters of a radio communications system is made possible by changing such control information as described above. Furthermore, the cognitive pilot channel may be applied without changing the terminal apparatus itself.
Therefore, adopting the present technique makes it possible to decrease the price of the terminal apparatus and to deal with changing of the radio communications system parameters. Moreover, as dealing with changing the radio communications system parameter is made possible, it is possible to expect an increase in frequency utilization efficiency.
In the present technique, an area covered by a base station apparatus is divided into multiple portions, each of which may also be called a mesh. In the area covered by the base station, a control signal is transmitted, and then, radio resource utilization methods such as radio communications system basic parameter information are reported multiple times mesh by mesh. Information reported may be the same. Moreover, as a method of distributing a control signal, there are two types, a broadcast-type distribution method and an on-demand type distribution method. In the broadcast-type distribution method, the base station apparatus periodically distributes control information corresponding to the mesh within a region which the base station apparatus is in charge of. In the on-demand type distribution method, the base station apparatus distributes control information for the mesh requested by the terminal apparatus in response to a request for distribution from a terminal apparatus. Moreover, a Hierarchical Advertiser CPC is being proposed in which some control signals to be distributed are divided and multiple distribution stations and units are utilized.
Non-Patent Document 1:    J. Perez-Romero, et al., “A Novel On-Demand Cognitive Pilot Channel enabling Dynamic Spectrum Allocation,” IEEE Dyspan 2007.